This invention relates to the art of polysulfide polymers, more particularly to thiol terminated liquid polysulfide polymers and hot melt applications, such as, hot melt applied sealants, extrusion of hoses and the like.
The use of thiol terminated liquid polysulfide polymer in caulks, sealants, and the like for numerous applications is well known. Such materials have normally, until now, been applied as liquids and chemically cured to solids in situ.
If rapid cure was desired, a two part system was employed, requiring mixing with proper equipment just before use. One part chemical cure, on the other hand, was satisfactory in avoiding the need for in situ mixing but inherently was a slower cure requiring that provision be made for time to reach structural integrity, in some uses requiring provision of storage facilities, support racks and the like. In production applications, the extra space and/or equipment required by either cure mechanism added a cost factor whose elimination would be considered desirable by those skilled in the art.
Hot melt applied materials offer the potential to avoid both the two part chemical cure requirement of in situ mixing and the lengthy holding requirement of one part chemical cure.
Although polysulfide rubbers are classified along with most other natural and synthetic rubbers as thermoplastic materials, they have always been considered as sharing the property of most rubbers that once vulcanized they cannot be induced to flow under heat and pressure without extensive degradation of the basic polymeric chain and consequent permanent loss of most or all physical properties.
Until now, the available hot melt sealants, such as butyl based materials, have not exhibited good structural properties on cooling and have required cumbersome mechanical retention systems or the application of a second curable sealant with adequate mechanical properties where structural support is required as in insulated glass window sandwiches. The present invention provides the convenience of hot melt application with the good structural properties of polysulfide rubber.
U.S. Pat. No. 3,243,403, a copy of which accompanies this application, is concerned with and claims the cure of thiol terminated liquid polysulfide polymers with dibutyl tin oxide and the cured product obtained thereby. There is no teaching or suggestion in said patent or in any prior art of which applicant is aware that dibutyl tin oxide cured polysulfide polymers have any different reaction to the application of heat and pressure to them than other known cured polysulfide rubbers.